1. Field of the Invention
The present invention relates to a multi-beam scanning optical apparatus and image forming apparatus using the same and, more particularly, to an image forming apparatus such as a laser beam printer having, e.g., an electrophotographic process, digital copying machine, or multi-functional printer, in which a plurality of light beams emitted from a light source means having a plurality of light emitting portions are deflected by a polygon mirror serving as an optical deflector and then caused to be optically scanned on a surface to be scanned through scanning optical means having an f-θ characteristic so as to record image information.
2. Related Background Art
A scanning optical apparatus (scanning optical system) conventionally used for an image forming apparatus is often designed to guide a light beam emitted from light source means to deflection means through an incident optical means and to form and scan the spot image of the light beam deflected by the deflection means on a surface to be scanned through scanning optical means having an f-θ characteristic.
Along with the recent improvement in performance and multi-functional ability of image forming apparatuses, scanning optical apparatuses are also required to operate at a high speed. To meet this requirement for high-speed operation, a plurality of light sources (light emitting portions) are used. In, e.g., Japanese Patent Application Laid-Open No. 9-54263, a multi-beam laser chip for emitting a plurality of linearly arranged light beams (laser beams) from one chip is used as light source means.
In an image forming apparatus, generally, if the interval between scanning lines in the sub scanning direction changes depending on position due to various reasons, the printed image quality degrades. Especially, this phenomenon readily takes place in a multi-beam scanning optical apparatus having a plurality of light emitting portions because of the presence of the plurality of light emitting portions.